Original Research

Performance of Xpert® MTB/RIF among tuberculosis outpatients in Lilongwe, Malawi

Tarsizio Chikaonda, Nelson Nguluwe, Brian Barnett, Runa H. Gokhale, Robert Krysiak, Isaac Thengolose, Nora E. Rosenberg, Christopher Stanley, James Mpunga, Irving F. Hoffman, Mina Hosseinipour, Lesley Scott, Wendy Stevens
African Journal of Laboratory Medicine | Vol 6, No 2 | a464 | DOI: https://doi.org/10.4102/ajlm.v6i2.464 | © 2017 Tarsizio Chikaonda, Nelson Nguluwe, Brian Barnett, Runa H. Gokhale, Robert Krysiak, Isaac Thengolose, Nora E. Rosenberg, Christopher Stanley, James Mpunga, Irving F. Hoffman, Mina Hosseinipour, Lesley Scott, Wendy Stevens | This work is licensed under CC Attribution 4.0
Submitted: 08 April 2016 | Published: 31 March 2017

About the author(s)

Tarsizio Chikaonda, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, School of Pathology, University of the Witwatersrand, Johannesburg, South Africa and University of North Carolina Project, Lilongwe, Malawi
Nelson Nguluwe, University of North Carolina Project, Lilongwe, Malawi
Brian Barnett, University of North Carolina Project, Lilongwe, Malawi
Runa H. Gokhale, University of North Carolina Project, Lilongwe, Malawi
Robert Krysiak, University of North Carolina Project, Lilongwe, Malawi
Isaac Thengolose, University of North Carolina Project, Lilongwe, Malawi
Nora E. Rosenberg, University of North Carolina Project, Lilongwe, Malawi
Christopher Stanley, University of North Carolina Project, Lilongwe, Malawi
James Mpunga, Malawi National Tuberculosis Programme, Lilongwe, Malawi
Irving F. Hoffman, Department of Molecular Medicine and Haematology, Faculty of Health Sciences,School of Pathology, University of the Witwatersrand, Johannesburg, South Africa and University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Mina Hosseinipour, Department of Molecular Medicine and Haematology, Faculty of Health Sciences,School of Pathology, University of the Witwatersrand, Johannesburg, South Africa and University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Lesley Scott, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, School of Pathology, University of the Witwatersrand, Johannesburg, South Africa
Wendy Stevens, Department of Molecular Medicine and Haematology, Faculty of Health Sciences, School of Pathology, University of the Witwatersrand, Johannesburg, South Africa


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Abstract

Background: Xpert® MTB/RIF is a molecular test for the detection of Mycobacterium tuberculosis and rifampicin resistance. It is considered to be a great advance over smear microscopy and culture. However, there is very little information regarding the performance characteristics of Xpert MTB/RIF in Malawi.

Objective: We aimed to evaluate the performance of Xpert MTB/RIF in a Malawian setting.

Methods: Stored sputum pellets were processed on Xpert MTB/RIF between June 2012 andMay 2014. Results were compared to mycobacteria growth indicator tube and Löwenstein-Jensen cultures, LED fluorescent microscopy and GenoType® MTBDRplus assay. Rifampicinresistance was confirmed by DNA sequencing.

Results: Of the 348 specimens with valid Xpert MTB/RIF results, 129/348 (37%) were smearpositive and 198/348 (57%) were culture-positive. Xpert MTB/RIF demonstrated a sensitivity of 93.8% (95% CI 89.4% – 96.8%) and specificity of 97.4% (95% CI 93.5% – 99.3%), with a positive predictive value of 97.8% (95% CI 94.6% – 99.4%) and a negative predictive value of 92.6% (95% CI 87.4% – 96.1%). Xpert MTB/RIF correctly identified 185/186 (99.5%) rifampicin sensitive and 2/2 (100%) rifampicin-resistant M. tuberculosis strains. Mutations were notdetected by sequencing in one isolate which was rifampicin resistant on Xpert MTB/RIF butsensitive on MTBDRplus. Four non-tuberculous mycobacteria grew from four smear-negativespecimens, namely, M. avium (n = 1) and M. intracellulare (n = 3). No cross-reactivity wasobserved with any of the non-tuberculous mycobacteria when using Xpert MTB/RIF.

Conclusion: When fully implemented, Xpert MTB/RIF may have an impact on patient care inMalawi. The increased diagnostic yield of Xpert MTB/RIF over smear microscopy can increaselaboratory-confirmed tuberculosis detection and ensure that treatment is given to appropriateindividuals or groups.


Keywords

Mycobacterium Tuberculosis; Rifampicin resistance; rpoB mutation

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